1. Field of the Invention
The present invention relates to a semiconductor radioactive ray detector for use in detection of such radioactive rays as X-rays or gamma rays by cooling the detector element to a cryogenic temperature near to that of liquid nitrogen (77K) and more particularly to a semiconductor radioactive ray detector which uses electricity instead of liquid nitrogen which has been conventionally used for cooling the detector element. The semiconductor radioactive ray detector of the present invention can be widely applied not only in measurement of such radioactive rays as gamma rays, X-rays or the like in nuclear reactor associated facilities but also in the field of radioactive ray measurement for nuclear physics, astrophysics, nuclear chemistry, etc.
2. Prior Art
FIG. 1 illustrates a liquid nitrogen cooled type semiconductor radioactive ray detector which has been conventionally used. In FIG. 1, numeral 101 designates a semiconductor radioactive detecting element, numeral 102 a cooling vessel, numeral 103 liquid nitrogen, numeral 104 a cooling rod, numeral 105 a semiconductor radioactive ray detector vessel and numeral 106 a signal preamplifier. As shown in FIG. 1, according to the semiconductor radioactive ray detector which has hithertofore been used, the semiconductor radioactive ray detector element 101 (such as Ge detecting element, Si detecting element or the like) has been cooled by using the cooling vessel 102 containing liquid nitrogen 103. Since liquid nitrogen is required to be used, it has to be made available before use, which has made it difficult to use such a detector readily and limited the place of where such a detector is used. Besides, since the cooling vessel 102 has to be used, miniaturization of such a detector as a whole has been difficult.
Consequently, an electric-cooled semiconductor radioactive ray detector has been developed, the detector using a closed-cycle He refrigerator for cooling the semiconductor radioactive detecting element.
FIG. 2 illustrates an electric-cooled semiconductor radioactive ray detector using such a closed-cycle He refrigerator. In FIG. 2, the same reference numerals as those used in FIG. 1 designate the same elements as those designated by the corresponding numerals in FIG. 1. In FIG. 2, reference numeral 107 designates a compressor for the closed-cycle refrigerator, numeral 108 a pipe, numeral 109 a cooling mechanism for the closed-cycle refrigerator which utilizes a Solvay cooling mechanism or the like, numeral 110 a cooler part, and numeral 111 cushioning member, respectively. In case of the electric-cooled semiconductor radioactive ray detector as shown in FIG. 2, it was difficult to make this semiconductor radioactive ray detector portable, because it is difficult to make the closed-cycle He refrigerator miniaturized and this refrigerator was also so heavy. Furthermore, in the case of the closed-cycle He refrigerator, microphonics is generated by the vibrational noise generated at the cooler part 110. Microphonics are causes of degradation of the energy resolution. Since frequency band of the microphonics thus generated is expanded originating in the cooling method to the frequency band close to that of the radioactive ray signals, it was difficult to remove such microphonics only by means of signal processing technology. Accordingly, a cushioning member 111 such as a vibration absorbing material or the like adapted to absorb vibrational noise was interposed between the semiconductor radioactive detecting element 101 and the cooler part 110 so as to remove the influence of microphonics. Since such a cushioning member 111 as a vibration absorbing material or the like has to be used and the cooling capacity of the refrigerator has to be secured for cooling of the semiconductor radioactive ray detecting element 101 and compensation for the loss due to the cushioning member 111 such as a vibration absorbing material or the like, a large cooling capacity has to be provided, which also made it difficult for the refrigerator to be miniaturized.